I answer that, Spiritual sins are of greater guilt than carnal sins: yet this does not mean that each spiritual sin is of greater guilt than each carnal sin; but that, considering the sole difference between spiritual and carnal, spiritual sins are more grievous than carnal sins, other things being equal. Three reasons may be assigned for this. The first is on the part of the subject: because spiritual sins belong to the spirit, to which it is proper to turn to God, and to turn away from Him; whereas carnal sins are consummated in the carnal pleasure of the appetite, to which it chiefly belongs to turn to goods of the body; so that carnal sin, as such, denotes more a turning to something, and for that reason, implies a closer cleaving; whereas spiritual sin denotes more a turning from something, whence the notion of guilt arises; and for this reason it involves greater guilt. A second reason may be taken on the part of the person against whom sin is committed: because carnal sin, as such, is against the sinner's own body, which he ought to love less, in the order of charity, than God and his neighbor, against whom he commits spiritual sins, and consequently spiritual sins, as such, are of greater guilt. A third reason may be taken from the motive, since the stronger the impulse to sin, the less grievous the sin, as we shall state further on (A. 6). Now carnal sins have a stronger impulse, viz. our innate concupiscence of the flesh. Therefore spiritual sins, as such, are of greater guilt.
Reply Obj. 1: Adultery belongs not only to the sin of lust, but also to the sin of injustice, and in this respect may be brought under the head of covetousness, as a gloss observes on Eph. 5:5. "No fornicator, or unclean, or covetous person," etc.; so that adultery is so much more grievous than theft, as a man loves his wife more than his chattels.
Reply Obj. 2: The devil is said to rejoice chiefly in the sin of lust, because it is of the greatest adhesion, and man can with difficulty be withdrawn from it. "For the desire of pleasure is insatiable," as the Philosopher states (Ethic. iii, 12).
Reply Obj. 3: As the Philosopher himself says (Ethic. vii, 6), the reason why it is more shameful to be incontinent in lust than in anger, is that lust partakes less of reason; and in the same sense he says (Ethic. iii, 10) that "sins of intemperance are most worthy of reproach, because they are about those pleasures which are common to us and irrational animals": hence, by these sins man is, so to speak, brutalized; for which same reason Gregory says (Moral. xxxi, 17) that they are more shameful. ________________________
SIXTH ARTICLE [I-II, Q. 73, Art. 6]
Whether the Gravity of a Sin Depends on Its Cause?
Objection 1: It would seem that the gravity of a sin does not depend on its cause. Because the greater a sin's cause, the more forcibly it moves to sin, and so the more difficult is it to resist. But sin is lessened by the fact that it is difficult to resist; for it denotes weakness in the sinner, if he cannot easily resist sin; and a sin that is due to weakness is deemed less grievous. Therefore sin does not derive its gravity from its cause.
Obj. 2: Further, concupiscence is a general cause of sin; wherefore a gloss on Rom. 7:7, "For I had not known concupiscence," says: "The law is good, since by forbidding concupiscence, it forbids all evils." Now the greater the concupiscence by which man is overcome, the less grievous his sin. Therefore the gravity of a sin is diminished by the greatness of its cause.
Obj. 3: Further, as rectitude of the reason is the cause of a virtuous act, so defect in the reason seems to be the cause of sin. Now the greater the defect in the reason, the less grievous the sin: so much so that he who lacks the use of reason, is altogether excused from sin, and he who sins through ignorance, sins less grievously. Therefore the gravity of a sin is not increased by the greatness of its cause.
On the contrary, If the cause be increased, the effect is increased. Therefore the greater the cause of sin, the more grievous the sin.